Radical Initiator Research Articles

Radicals in Annulation of Mixed Benzoyl Phosphonium‐Iodonium Ylide and Acetylenes Explored by EPR‐ST Spectroscopy

AbstractAnnulation of mixed phosponium‐iodonium ylides and compounds with a triple bond is an interesting example of the synthesis of different types of heterocycles in one‐pot, metal‐free systems at ambient temperature to give substituted oxazoles in the reaction with nitriles and phosphorus‐containing λ5‐phosphinolines and substituted furans in the reaction with acetylenes. The iodonium group in the mixed ylides provides the possibility for the radical initiation of the reaction. Herein, we investigated the generation of primary radicals and the formation of phosphorus‐containing products in the photolysis of benzoyl phosphonium‐iodonium ylide alone and in its reaction with acetylenes in DCM by EPR and 31P NMR spectroscopies with the use of two most popular spin traps, PBN and DMPO. The results allowed us to account the crucial difference in the registered radicals in the two systems for the aggregation of the components, with ylide molecules forming a core and acetylene molecules being a shell of the aggregates in DCM, in which the annulation occurs. The peculiarities of the reactions of PBN and DMPO with generated radicals are discussed.

Oligomerization of Fischer-Tropsch Olefins by Radical Initiation Method for Synthesizing Poly Olefin Base Oils

In the present work we have investigated the oligomerization process of Fischer-Tropsch synthesis products – gasoline (C5-C10) and diesel (C11-C18) hydrocarbon fractions with a total olefin content (consisting mainly olefins with a branched isomeric chain) of 79.3 and 31.8 wt.%, respectively. Oligomerization was carried out by radical initiation method using azobisisobutyronitrile, benzoyl peroxide, dicumyl peroxide and methyl ethyl ketone peroxide (Butanox M-50) as initiators. It was established that the yield of the oligomerization process depending on the initiator used decreases in the following order: azobisisobutyronitrile > benzoyl peroxide > dicumyl peroxide > Butanox M-50. It was determined that when the oligomerization is carried out in polar solvents such as acetone and dichloromethane the yield of product increases by ~2.1 and ~1.7 times, respectively, while at the same time adding a non-polar solvent such as tetrachloromethane to the reaction mixture decreases the product yield by ~2.0 times. The optimal technological parameters for carrying out oligomerization process of synthetic gasoline and diesel fractions were determined: where azobisisobutyronitrile, content 0.5 wt.%., is used as an initiator, acetone as solvent, with reaction temperature of 200 °C, and duration of 12 hrs. under inert atmosphere. The product yield from the diesel fraction is 39.5 %, and from the synthetic gasoline fraction – 36.0 %. At the same time, in terms of characteristics, the oligomerization product of the diesel fraction showed properties similar to commercially available Base oil 3cSt (Group III), and the gasoline fraction showed properties on par with the commercially produced PAO-2 (Group IV). Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Metal-Free Selective Air-oxidation of Sulfides to Sulfoxides Using V-70 [2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile)] and Isobutyraldehyde

Selective oxidation of sulfides to sulfoxides using “air” was achieved using a combination of V-70 [2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile)] (a radical initiator) and isobutyraldehyde (a co-oxidant). Various sulfides were successfully converted into their corresponding sulfoxides using this method. This approach promotes a sustainable oxidation process by excluding harmful oxidants, such as peroxides and metal reagents.

Intermolecular Sulfenoamination of Alkenes with Free-Thiols and NIS to Access β-Succinimide Sulfides.

A convenient and practical multicomponent strategy for the sulfenoamination of alkenes was realized, which using free-thiols as the sulfur-reagent, NIS both as radical initiator and an N-nucleophile. This protocol excellent in terms of transition-metal-free, good functional group tolerance, easily available substrates and facile scale-up. And provided a direct- and general way to synthesize various β-succinimide sulfides with high regioselectivity.

Tumor Receptor-Mediated Morphological Transformation and In Situ Polymerization of Diacetylene-Containing Lipidated Peptide Amphiphile on Cell Membranes for Tumor Suppression.

In situ polymerization on cell membranes can decrease cell mobility, which may inhibit tumor growth and invasion. However, the initiation of radical polymerization traditionally requires exogenous catalysts or free radical initiators, which might cause side effects in normal tissues. Herein, we synthesized a Y-type diacetylene-containing lipidated peptide amphiphile (TCDA-KFFFFK(GRGDS)-YIGSR, Y-DLPA) targeting integrins and laminin receptors on murine mammary carcinoma 4T1 cells, which underwent nanoparticle-to-nanofiber morphological transformation and in situ polymerization on cell membranes. Specifically, the polymerized Y-DLPA induced 4T1 cell apoptosis and disturbed the substance exchange and metabolism. In vitro assays demonstrated that the polymerized Y-DLPA nanofibers decreased the migration capacity of 4T1 cells, potentially suppressing tumor invasion and metastasis. When administered locally to 4T1 tumor-bearing mice, the Y-DLPA nanoparticles formed a biomimetic extracellular matrix that effectively suppressed tumor growth. This study provides an in situ polymerization strategy that can serve as an effective drug-free biomaterial with low side effects for antitumor therapy.

Investigation of the Cyclohexene Oxidation Mechanism Through the Direct Measurement of Organic Peroxy Radicals.

Monoterpenes, the second most abundant biogenic volatile organic compounds globally, are crucial in forming secondary organic aerosols, making their oxidation mechanisms vital for addressing climate change and air pollution. This study utilized cyclohexene as a surrogate to explore first-generation products from its ozonolysis through laboratory experiments and mechanistic modeling. We employed proton transfer reaction mass spectrometry with NH4+ ion sources (NH4+-CIMS) and a custom-built OH calibration source to quantify organic peroxy radicals (RO2) and closed-shell species. Under near-real atmospheric conditions in a Potential Aerosol Mass-Oxidation Flow Reactor, we identified 30 ozonolysis products, expanding previous data sets of low-oxygen compounds. Combined with simulations based on the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere and relevant literature, our results revealed that OH dominates over ozone in cyclohexene oxidation at typical atmospheric oxidant levels with H-abstraction contributing 30% of initial RO2 radicals. Highly oxidized molecules primarily arise from RO2 autoxidation initiated by ozone, and at least 15% of ozone oxidation products follow the overlooked nonvinyl hydroperoxides pathway. Gaps remain especially in understanding RO2 cross-reactions, and the structural complexity of monoterpenes further complicates research. As emissions decrease and afforestation increases, understanding these mechanisms becomes increasingly critical.

Selective recovery of Au from waste printed circuit board by water-soluble organic leaching: The key role of in situ bromine mediation and identificationof pathway

A large amount of gold in electronic waste (E-waste) is not properly recovered owing to the absence of efficient and safe leaching methods. Herein, we proposed the concept of ‘water-soluble organic Au leaching’ and created a new water-soluble organic leaching agent, WS NBS–DMF, by dissolving millimolar amounts of N-bromosuccinimide (NBS) and dimethylformamide (DMF) in water. Under mild conditions (25 ℃, pH 7.0), WS NBS–DMF achieved a 94.9 % leaching efficiency of Au for waste printed circuit board (WPCB) with limited leaching of base metals. The potent bromine radical (Br•) and ligands significantly contributed to Au complexation and oxidization via in situ bromine generation and radical initiation from WS NBS–DMF. The bidirectional hydrogen-bond effect of DMF facilitated the in situ bromine generation. Two Au(I) complexes ([AuBr2]- and [(NHS)AuBr]-) and an Au(III) complex ([(NHS)AuBr3]-) were confirmed as the Au leaching products by spectroscopy and mass spectrometry. Furthermore, reciprocal σ-donations between the Au center and ligands in the bonding orbitals enhanced the stability of the Au complexes, thereby promoting efficient Au leaching. Comparing with other leaching methods, this study of WS NBS–DMF provides a safe, economic and eco-friendly technique for efficient and selective gold recovery from e-waste.

Photoinduced Radical Approach for Desulfurative Alkylation of Cysteine Derivatives to Make Unnatural Amino Acids.

Unnatural amino acids (UAAs) are highly valuable molecules in organic synthesis, pharmaceutical sciences, and material science. Herein, we present a photocatalytic radical approach for desulfurative alkylation of cysteine derivatives with arenethiol as the hydrogen atom transfer catalyst for making UAAs and peptides. The formate salt, acting as the hydrogen atom donor, in situ generates the highly reductive CO2 radical anion species, which is the key to unlocking the C-S bond cleavage process with a simple benzoyl protecting group. No photocatalyst is required for the radical initiation and propagation, which makes such a visible-light-induced process mild, efficient, and sustainable.

Radical Reactions with Chiral Acylammonium Salts: Synthesis of Functionalized δ-Lactams through Giese-Initiated Organocascades.

Enantioselective Giese reactions employing chiral α,β-unsaturated acylammonium salts and subsequent diastereoselective trapping followed by lactamization deliver optically active δ-lactams. Alkyl iodides bearing tosylamides undergo radical initiation using triethylborane at low temperatures to provide carbon-centered radicals to initiate the described organocascade. Subsequent diastereoselective inter- or intramolecular trapping of the incipient α-radical leads to highly functionalized, enantioenriched mono- and bicyclic δ-lactams (up to 99:1 er, > 19:1 dr) bearing up to three stereogenic centers. Interestingly, benzotetramisole imparts diastereoselectivity that contradicts steric considerations alone. Results from DFT calculations rationalized the observed enantio- and diastereoselectivities, revealed an electrostatic interaction between the sulfone oxygens and the ammonium cation in the initial α-radical intermediate, and aided in application of this methodology to bicyclic δ-lactams through intramolecular trapping of the α-radical intermediate.

Carbon fiber/nano SiO2 reinforced polyelectrolyte-graft UHMWPE for water lubricated superlubricity

In this study, a new kind of UHMWPE composite with ultralow coefficient of friction (COF) and high mechanical properties was developed. An efficient method was established to graft hydrophilic monomer 3-sulfopropyl methacrylate potassium salt (SPMK) onto UHMWPE powder by thermal initiation radical polymerization. The COF of UHMWPE grafted SPMK sample was significantly reduced by 50 %. After filling carbon fiber and nano SiO2, the COF of UHMWPE composites can be reduced as low as 0.009 at 0.1 m/s. Besides, a 76.1 % decrease in wear rate of single UHMWPE was achieved. The outstanding tribological properties of UHMWPE composite was attributed to the synergistic effect of hydration lubrication and particle reinforcement. The prepared UHMWPE composite has great potential to realize water lubricated bearing.

Living Cell-Mediated Catalyst-Free Spontaneous Polymerization of Zwitterionic Methacrylates for Preparation of Probiotic-Loaded Hydrogels.

Living cell-mediated polymerization offers promising applications in biomaterials, yet its further biological utilization is hindered by the need for metal ions or radical initiators with available methods. In this study, we introduce a living cell-mediated polymerization that leverages the intrinsic metabolic activities of living cells to initiate and sustain free radical polymerization of zwitterionic methacrylates. The polymerization proceeded in the absence of transition metal catalysts, radical initiators, or light sources. The conversion of zwitterionic methacrylate strongly correlated with cellular activities and achieved a maximum conversion of 98% within 48 hours. Living cells efflux redox power across membranes through metabolism and that terminal electron fluxes are captured by zwitterionic methacrylates pre-assembled on the living cell surface to initiate radical polymerization reactions. The polymerization caused significant changes to the cell membrane surface and synthesized hydrogels with tailored mechanical properties. The polymer hydrogel obtained via probiotic E. coli Nissle 1917 was able to release the in-situ encapsulated molecules, which demonstrated living cell-mediated polymer hydrogel as a vehicle for the delivery of both cellular and molecular therapeutic agents. This research offered a green and efficient method for synthesizing bioactive materials and advancing the field of cellular therapeutics and drug delivery.

Bright Nanocomposites based on Quantum Dot‐Initiated Photocatalysis

Integrating quantum dots (QDs) into polymer matrix to form nanocomposites without compromising the QD photoluminescence (PL) is crucial to emerging QD light‐emitting and solar energy conversion fields. However, the most widely‐used bulk polymerization technique, where monomers serve as the QD solvent, usually leads to QD PL quenching caused by radical initiators. Here we demonstrate high‐brightness nanocomposites with near‐unity PL quantum yield (QY), through a novel QDs‐catalyzed (‐initiated) bulk polymerization without using any radical initiators. Different from previous reports where QDs were designed as photo‐sensitizers/catalysts (always with cocatalysts) and hence non‐emissive in catalytic conditions, our QDs combine high brightness with highly effective catalysis, a combination that was previously considered to be hardly possible. In our case, apart from emitting light (at a large probability), the photoexcited QDs act as ‘overall reaction’ catalysts by simultaneously employing photoexcited electrons and holes to produce active radicals without the need of any sacrificial agents. These active radicals, though with a small amount, are sufficient to initiate effective chain reaction‐dominated bulk polymerization, eliminating the requirement of extra radical initiators. This study provides new insights for understanding and development of QDs for energy applications.

Bright Nanocomposites based on Quantum Dot-Initiated Photocatalysis.

Integrating quantum dots (QDs) into polymer matrix to form nanocomposites without compromising the QD photoluminescence (PL) is crucial to emerging QD light-emitting and solar energy conversion fields. However, the most widely-used bulk polymerization technique, where monomers serve as the QD solvent, usually leads to QD PL quenching caused by radical initiators. Here we demonstrate high-brightness nanocomposites with near-unity PL quantum yield (QY), through a novel QDs-catalyzed (-initiated) bulk polymerization without using any radical initiators. Different from previous reports where QDs were designed as photo-sensitizers/catalysts (always with cocatalysts) and hence non-emissive in catalytic conditions, our QDs combine high brightness with highly effective catalysis, a combination that was previously considered to be hardly possible. In our case, apart from emitting light (at a large probability), the photoexcited QDs act as 'overall reaction' catalysts by simultaneously employing photoexcited electrons and holes to produce active radicals without the need of any sacrificial agents. These active radicals, though with a small amount, are sufficient to initiate effective chain reaction-dominated bulk polymerization, eliminating the requirement of extra radical initiators. This study provides new insights for understanding and development of QDs for energy applications.

Living Cell‐Mediated Catalyst‐Free Spontaneous Polymerization of Zwitterionic Methacrylates for Preparation of Probiotic‐Loaded Hydrogels

Living cell‐mediated polymerization offers promising applications in biomaterials, yet its further biological utilization is hindered by the need for metal ions or radical initiators with available methods. In this study, we introduce a living cell‐mediated polymerization that leverages the intrinsic metabolic activities of living cells to initiate and sustain free radical polymerization of zwitterionic methacrylates. The polymerization proceeded in the absence of transition metal catalysts, radical initiators, or light sources. The conversion of zwitterionic methacrylate strongly correlated with cellular activities and achieved a maximum conversion of 98% within 48 hours. Living cells efflux redox power across membranes through metabolism and that terminal electron fluxes are captured by zwitterionic methacrylates pre‐assembled on the living cell surface to initiate radical polymerization reactions. The polymerization caused significant changes to the cell membrane surface and synthesized hydrogels with tailored mechanical properties. The polymer hydrogel obtained via probiotic E. coli Nissle 1917 was able to release the in‐situ encapsulated molecules, which demonstrated living cell‐mediated polymer hydrogel as a vehicle for the delivery of both cellular and molecular therapeutic agents. This research offered a green and efficient method for synthesizing bioactive materials and advancing the field of cellular therapeutics and drug delivery.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source.

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Xanthenes: Novelty and Green Photocatalysis for the Formation of Carbon-carbon or Carbon-heteroatom Bond

: This review covers photoreduction reactions using xanthenes reported from 2011 to date and compares them with the conventional photocatalytic method. Xanthenes have strong absorption in the visible light spectrum (520-550 nm), and their redox potential resembles organometallic complexes, such as those containing Ir or Ru, and they are also easy to handle and accessible. In addition to being metal-free, photocatalysis with xanthenes is performed under mild reaction conditions. For instance, no radical initiators are needed because the energy sources are led devices or household lamps, most reactions are performed at room temperature in common solvents (MeOH, MeCN, acetone, DMSO), and an anhydrous or inert atmosphere is usually not required. As a result, xanthene dyes hold the promise of a more environmentally friendly synthesis of organic compounds.

Scavenging of Alkylperoxyl Radicals by Addition to Ascorbate: An Alternative Mechanism to Electron Transfer.

Vitamin C (ascorbate; Asc) is a biologically important antioxidant that scavenges reactive oxygen species such as deleterious alkylperoxyl radicals (ROO•), which are generated by radical-mediated oxidation of biomolecules in the presence of oxygen. The radical trapping proprieties of Asc are conventionally attributed to its ability to undergo single-electron transfers with reactive species. According to this mechanism, the reaction between Asc and ROO• results in the formation of dehydroascorbate (DHA) and the corresponding hydroperoxides (ROOH). When studying the reactivity of DNA 5-(2'-deoxyuridinyl)methylperoxyl radicals, we discovered a novel pathway of ROO• scavenging by Asc. The purpose of this study is to elucidate the underlying mechanism of this reaction with emphasis on the characterization of intermediate and final decomposition products. We show that the trapping of ROO• by Asc leads to the formation of an alcohol (ROH) together with an unstable cyclic oxalyl-l-threonate intermediate (cOxa-Thr), which readily undergoes hydrolysis into a series of open-chain oxalyl-l-threonic acid regioisomers. The structure of products was determined by detailed MS and NMR analyses. The above transformation can be explained by initial peroxyl radical addition (PRA) onto the C2=C3 enediol portion of Asc. Following oxidation of the resulting adduct radical, the product subsequently undergoes Baeyer-Villiger rearrangement, which releases ROH and generates the ring expansion product cOxa-Thr. The present investigation provides robust clarifications of the peroxide-mediated oxidation chemistry of Asc and DHA that has largely been obscured in the past by interference with autooxidation reactions and difficulties in analyzing and characterizing oxidation products. Scavenging of ROO• by PRA onto Asc may have beneficial consequences since it directly converts ROO• into ROH, which prevents the formation of potentially deleterious ROOH, although it induces the breakdown of Asc into fragments of oxalyl-l-threonic acid.

Lignin‐Based Macromolecular Photoinitiator for Non‐Migration, Self‐Adhesive, and Water‐Resistant Eutectogels toward Underwater Reliable Communication

AbstractHydrophobic conductive gels have attracted much attention in underwater sensing as the soft robots and wearable sensors. Among the various methods for preparing conductive gels, UV‐initiated polymerization shows advantages of rapid curing and significant energy savings. However, traditional commonly used photoinitiators in UV‐initiated polymerization often migrate or diffuse within conductive gels, especially with prolonged use or underwater, posing potential environmental and health risks. Herein, a novel lignin‐based macromolecular photoinitiator (L‐BF) is first designed by incorporating benzoylformate into the lignin backbone, demonstrating excellent UV absorption, high radical initiation efficiency, and hydrophobicity. Subsequently, hydrophobic eutectogels (HEG) are prepared via UV‐initiated polymerization using L‐BF as photoinitiator. The HEG shows excellent mechanical properties (toughness of 5.67 MJ m−3 and strain of 941%) and scarcely L‐BF migration underwater. Moreover, the hydrophobic network of L‐BF endowed HEG with hydrophobicity (water contact angle exceeds 110°; swelling ratio is <5.8%), superior underwater adhesion (255 kPa), even maintained excellent sensing performance (gauge factor of 4.69), and long‐term reproducibility (20 000 cycles) in air and underwater. Validation confirms the potential of HEG as an effective wearable sensor for underwater posture monitoring and communication, advancing the use of lignin and low‐migration conductive gels in marine exploration.

Sequential therapy for extramedullary plasmacytoma of the palate: a rare case report with seven years of follow-up and literature review

BackgroundExtramedullary plasmacytoma (EMP) is a rare solitary malignancy that accounts for 3% of plasma cell neoplasms, and EMP with a primary occurrence in the palate is extremely uncommon. Owing to the long course of EMP and the limited available data on treatment outcomes, there are no definitive guidelines for its management, especially for high-risk patients who are more susceptible to early progression to multiple myeloma.Case presentationIn this study, we review nine relevant studies and describe a 54-year-old woman who presented with an asymptomatic nonulcerative mass localized in the palate. After initial radical surgical resection of the lesion, the patient was definitively diagnosed with EMP with minimal plasmacytosis in the bone marrow, and adjuvant intensity-modulated radiation therapy with a minimum dose of 39.6 Gy was administrated in the surgical area. There was no evidence of local recurrence, nodal metastasis or progression to multiple myeloma (MM) during the seven-year follow-up period.ConclusionGiven the atypical clinical features of palate EMP reported in the literature and the encouraging results of our patient, sequential therapy involving surgery and adjuvant radiotherapy for primary palatal lesions in high-risk EMP patients without nodal involvement could be an effective treatment modality.

Isonitrile Photochemistry: A Functional Group Class Coming in from the Cold.

Starting from a historical background that acknowledges isonitriles as a neglected class of compounds due to their unpleasant smell and hardly controlled reaction conditions with open shell species, the present concept article aims at highlighting the seeds of the modern isonitrile photochemistry. Representative essential transformations achieved via either UV light irradiation or radical initiators at high temperatures are brought into play to draw a parallel with the current literature relying on the exploitation of visible light photochemical methods. Such a comparison points out the potential of this enabling technology to further expand the scope of isonitrile chemistry and the unmet challenges which makes it a very stimulating field.